In the next budget year we shall focus our efforts on three main objectives. 1. Further characterization of the cells which participate in the regulation and the effector phase of the anti-YAC immune responses. We shall try to determine the specificity of these cells by absorbing them into different tumor-monolayers and testing the function of the absorbed cells. In addition, we shall characterize other properties of the cells such as their sensitivity to irradiation, hydrocortizone, mitomycin c, BUDR and light, adult thymectomy, splenectomy and ATS treatment. We shall try to separate the different types of cells by velocity gradient. Some of these experiments may be extended to the third year of this project. 2. We shall try to protect mice from YAC tumor by preinjecting them with inactivated YAC-1. We shall also try to enhance the growth of low doses of living YAC tumor (which normally are rejected) by preinjecting the mice with inactivated YAC. Preliminary experiments have already been started. 3. We shall try to use purified cellular fractions of both YAC and YAC-1 for syngeneic immunization of A/J mice against the tumor. We shall try to identify the different immunogenic cellular fractions by using anti MCSA (Moloney cellular surface antigen), anti gp70, anti P15 and anti P30 as blockers of the immunogenic activity of the different cellular fractions. We shall try to determine what is the cellular fraction which is responsible for conferring rejectibility of tumor to the A/J mice. In addition, we shall try to detect, among the cellular fractions, a fraction with suppressogenic properties.